Pneumothorax. Coloured X-ray of the chest of a 76 year old with a pneumothorax, or collapsed lung. The arrows show where the left lung has collapsed due to a build-up of air between the lung and chest wall. Pneumothorax can be due to trauma or lung rupture. It causes shortness of breath and pain on breathing. It is treated by inserting a tube to drain the air over a period of days, allowing the lung to re-inflate.